linux-kernel - Re: [PATCH] x86: fix spin_is

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Message-ID: <20080805020758.GB15075@wotan.suse.de>
Date:	Tue, 5 Aug 2008 04:07:59 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix spin_is_contended()

On Mon, Aug 04, 2008 at 02:38:54PM +0100, Jan Beulich wrote:
> The masked difference is what needs to be compared against 1, rather
> than the difference of masked values (which can be negative).

Dang, thanks.

> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> Cc: Nick Piggin <npiggin@...e.de>
> 
> ---
>  include/asm-x86/spinlock.h |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- linux-2.6.27-rc1/include/asm-x86/spinlock.h	2008-07-31 17:08:34.000000000 +0200
> +++ 2.6.27-rc1-x86-spin-is-contended/include/asm-x86/spinlock.h	2008-08-04 11:09:33.000000000 +0200
> @@ -65,7 +65,7 @@ static inline int __ticket_spin_is_conte
>  {
>  	int tmp = ACCESS_ONCE(lock->slock);
>  
> -	return (((tmp >> 8) & 0xff) - (tmp & 0xff)) > 1;
> +	return (((tmp >> 8) - tmp) & 0xff) > 1;
>  }
>  
>  static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
> @@ -127,7 +127,7 @@ static inline int __ticket_spin_is_conte
>  {
>  	int tmp = ACCESS_ONCE(lock->slock);
>  
> -	return (((tmp >> 16) & 0xffff) - (tmp & 0xffff)) > 1;
> +	return (((tmp >> 16) - tmp) & 0xffff) > 1;
>  }
>  
>  static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
> 
> 
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